This invention relates to low molecular weight polymers of unsaturated dicarboxylic anhydrides with copolymerizable monomers and to a process for their preparation.
Polymers of unsaturated dicarboxylic acid anhydrides with copolymerizable monomers, such as copolymers of styrene and maleic anhydride, have been used in a wide variety of applications including coating and adhesive applications. In many of such uses, the efficacy for a particular purpose depends largely upon the molecular weight of such polymers. For example, for certain uses (e.g., as dispersants for pigments, slurries, grinding aids, etc.; as viscosity control agents in coating formulations; as embrittling agents in rug shampoos; and as emulsifying agents or protective colloids), it is necessary that such polymers have relatively low molecular weights.
Various techniques have been employed in the prior art to control the molecular weight of such polymers to the desired low level. Such prior art techniques have included the use of (A) high polymerization temperature; (B) high concentrations of free radical catalysts; (C) chain transfer agents, such as (1) mercaptans in solution polymerizations (U.S. Pat. No. 2,606,891), (2) ditertiary butyl parabenzoquinone in mass polymerizations (U.S. Pat. No. 2,640,819), (3) aldehydes (U.S. Pat. No. 2,938,016), and (4) cyclic molecular weight regulators (e.g., methylene cyclobutane, terpinolene, etc.) in high temperature mass polymerizations (U.S. Pat. No. 3,380,972); (D) chain terminating solvent systems (U.S. Pat. Nos. 2,913,437; 3,085,994; 3,342,787; and 3,392,155); and (E) special polymerization chronology (U.S. Pat. No. 2,744,098). In addition, hybrids of the foregoing individual techniques have been employed such as combined use of high temperature, specially controlled monomer feed, chain terminating solvents and polymer product precipitation. See, for example, U.S. Pat. Nos. 3,178,395; 3,451,979 and 3,558,570.
Unfortunately, however, all of such prior art techniques suffer one or more disadvantages such as high cost, production of colored products, retention of impurities in the resulting polymer, requirement of special solvents and difficult solvent removal, etc.
In view of the attendant disadvantages of the aforementioned prior art techniques, it would be highly desirable to provide an improved process for preparing low molecular weight polymers of unsaturated dicarboxylic anhydrides with copolymerizable monomers which improved process is free of such prior art deficiencies.